In my experience, any sealer that you apply will darken the wood to some degree. In addition, some sealers have a natural amber tint that changes the color of the wood. And thirdly, the degree of change depends on whether the sealer is applied as a top coat, or if it is applied as a sealer, and the the turning is sanded with a higher grade of abrasive. Keep in mind that surface gloss can affect the appearance of wood, and sanding to eliminate that gloss can have a dramatic effect. Ultimately, you have to experiment to develop an understanding of how specific finishes affect individual woods.
Two suggestions for you to consider. First, lacquer is essentially colorless. You can thin ordinary brushing lacquer (Deft or Watco) with lacquer thinner to produce a sealer. It will darken the wood slightly, and will enhance the grain. However, if you subsequently sand the item with a high-grade sandpaper to remove any surface gloss caused by the sealer, the 'darkening' effect will be minimized.
Another option is water-based polyurethane. This stuff is colorless - and when applied to very light timbers, it sometimes appear to have a very faint blue cast. But like lacquer, if you apply it as a sealer, allow it to cure, and the sand lightly with a high grit abrasive, you can restore much of the original appearance of the wood.